Adaptation vs Exaptation 1. Definition 1: Adaptation = A trait, or integrated suite of traits, that increases the fitness (reproductive success) of its possessor. 2. However, traits can have current utility (i.e. increase fitness), but may not have been selected for that function. 3. Definition 2: Adaptation = a trait shaped by natural selection for its current use. 4. Exaptation (pre-adaptation): a. Trait arises nonadaptively, but is co-opted for useful function later. b. Trait arises adaptively, but is co-opted for a new use. Examples of Exaptation 1. Spandrels 2. Feathers and flight 3. Snail that lays eggs in the center of its spiral 4. Dancing in cockatoos Lindberg and Doberteen 1981 Meet Snowball the cockatoo! Behavior of the Day! http://www.youtube.com/watch?v=hf7xttvu2sm http://www.nature.com/scitable/blog/student-voices/we_got_the_beat_and Historical Hypotheses 1. Definition 2: Adaptation = a trait shaped by natural selection for its current use. 2. This is a historical hypothesis: Must reconstruct evolutionary history to test it. 3. Also important to observe how evolution proceeds over time.
Lecture Outline Reasons for Lek Polygyny Alternative mating strategies Adaptive versus Non-adaptive hypotheses Using phylogenetics to test hypotheses in behavioral ecology Overview of Phylogenetics 1. A phylogeny, or evolutionary tree, represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa (singular: taxon). 2. The tips of the tree represent groups of descendent taxa (often species). 3. The nodes on the tree represent the common ancestors of those descendents. Overview of Phylogenetics 4. Two descendents that split from the same node are called sister groups. In the tree below, species A & B are sister groups they are each other's closest relatives. 5. Outgroup a taxon outside the group of interest. 6. All the members of the group of interest are more closely related to each other than they are to the outgroup. 7. The outgroup is useful when constructing evolutionary trees and determining how phenotypic traits have evolved over time. a. Example 1: Spider behavior Orb-weaving spiders, spin intricate and orderly webs. Other spiders spin disorderly cobweb-like webs. Hypothesis on which came first?
The Evolutionary History of Spiders and Web Making Cobweb Orb webs evolve (species in yellow) Cobweb Cobweb Dimitrov et al 2012 Tangled in a sparse spider web: single origin of orb weavers and their spinning work unravelled by denser taxonomic sampling 1. Hypothesis: Complex orb webs evolved from less complex cob webs. 2. Results from phylogenetic analysis: Orb-weaving was the ancestral state. Cobweb-weaving evolved from spiders with more orderly webs. Reject hypothesis. 3. Side lesson: Evolution does not always go from less to more complex. Sensory bias in Swordtails Test for the preference in closely related species that don t have the trait. Pre-existing preference is an exaptation. Occurred before it was used for sexual selection. Male sword is an adaptation to exploit the sensory bias of females. 2. Phylogenies can suggest evolutionary constraints. a. Pseudocopulation behavior in asexual whiptails. Their reproduction is constrained by their evolutionary history of once being sexual.
2. Phylogenies can suggest evolutionary constraints. 3. Phylogenies can be used to test evolutionary hypotheses. a. Want to compare behaviors and traits across species to test if they evolve together. b. Problem: Species are not independent data points because they share an evolutionary history. c. Solution: Compare independent evolutionary replicates of traits changing. Compare sister taxa with different traits. Phylogenies can be used to test evolutionary hypotheses 1. Analyses using correlations and regressions assume that the data points are independent. 2. Species data is not independent. For example, all gibbons are monogamous, eat fruit, and hold territories. Independent Contrasts Example of Independent Contrasts Changes in HVC volume are correlated with changes in repertoire size.
2. Phylogenies can suggest evolutionary constraints. a. Pseudocopulation behavior in asexual whiptails. Their reproduction is constrained by their evolutionary history of once being sexual. 3. Phylogenies can be used to test evolutionary hypotheses. 4. Phylogenies can reveal evolutionary patterns. Convergent Evolution 1. Traits can be shared among species because they have a common ancestor. a. All birds have feathers because they have the same common ancestor that had feathers. 2. Traits can be shared among species that are not closely related due to convergent evolution. a. Bats, birds, and pterodactyls all have wings. But wings independently evolved in all of these groups. 3. Convergent evolution: Similarity between species is caused by a similar, but evolutionarily independent, response to a common environmental problem. 4. Allows tests of the conditions that cause traits to evolve because evolution has been replicated. Convergent Evolution 1. Many mammals and marsupials have independently converged on similar morphologies due to similar ecologies. 2. Phylogenies can suggest evolutionary constraints. a. Pseudocopulation behavior in asexual whiptails. Their reproduction is constrained by their evolutionary history of once being sexual. b. Tradeoff between eyes and horns in dung beetles. 3. Phylogenies can reveal evolutionary patterns. a. Example: The evolutionary history of side-blotched lizard mating strategies.
O, B O, B O, B O, B O O
ob ob 1. Hypothesis 1: Having multiple mating strategies was ancestral, mating types have been lost over time. 2. Hypothesis 2: Multiple mating strategies built up over time from a more simple, monomorphic state. There are Eight Independent Losses of Mating Strategies and the Yellow Allele is Repeatedly Lost Tree Lizards Urosaurus ornatus 1. Result: Having multiple mating strategies was ancestral, mating types have been lost over time. 2. In all cases, the yellow allele has been lost from the population. 3. This is an example of convergent/replicated evolution.
Summary 1. Phylogenies are important for determining how traits evolve over time. 2. Phylogenies are important for rigorously testing hypotheses about adaptation. 3. Both adaptive and non-adaptive hypotheses can provide insight into evolution